Signal repeating system



H. R. HAYDEN SIGNAL REPEATING- SYSTEM Feb. 13, 19.34.

med sept. so, 19:52

MMAAAAMMA J W n Mw mm INVENToR fara/d @Haya/ef? BY m ATTORNEY PatentedFeb. 13, 1934 UNITED STATES PATENT oFFicE Application September 30, 1932Serial No. 635,509

7 Claims.'

Thisinvention relates to vacuum tube signal repeating systems and moreparticularly to an.

improved amplifying system.

In the specific embodiment of my .invention herein disclosed, the systemcomprises successive radio frequency amplifying stages, a detector stageand audio frequency amplifying stages.

One of the audio frequency amplifying stages is a push pull stage and myinvention consists in 10 part of an improved resistance or similarcoupling between the push pull stage and the preceding stage. Onecharacteristic of such a coupling is that the impulses transmitted tothe push pull are dependent upon variations of potential of points l5 Tnthe plate circuit of the preceding stage.

Among the objects of my invention is to provide -an improved receivingand reproducing system of this general character which is free fromdisturbing noises, such as may be caused by regeneration, feed back orhum derived from an alternating current source of supply-and further toprovide a system which will accurately reproduce n incoming signals overa wide frequency range.

The drawing shows diagrammatically one embodiment of my invention.l

The system disclosed in the drawing comprises three stages of radiofrequency amplification, a detector stage and two stages of audiofrequency amplication, the second of which is a push pull stage which asshown is coupled to a dynamic loud speaker. Power for energizing thesystem is supplied from alternating current lighting means which areconnected to a transformer AT and thence through a rectifier R to supplythe field coil F of a loud speaker L. A second transformer T is providedwith secondaries S and S1 for supplying alternating current for heatingthe tube cathodes, whilesecondaries S2 and S3 energize the plate andcathode heating circuits respectively of a rectifier tube R whichsupplies the plate circuits of the signal tubes through a filter F.

Reference character 10 represents an antenna for receiving signal wavesand Sw .a double throw switch designed to connect the antenna to groundthrough a tuning condenser l1, primary 12 of a transformer 13 and aresistance R2 shunted by a fixed condenser C1 of small capacity. A

tuning condenser 15 connects a point in the antenna circuit betweencondenser 11 and coil 12,

with ground. The secondary 16 of the transformer 13 isconnected at oneend to the grid of tube lRF and its oppositeend is connected to groundthrough condenser.C1 and resistance R2.

Grid of tube IRF is also connected to ground through a tuning condenser1'? shunted by a trimming condenser 14.

When it is desired to receive incoming signals without using the antenna10,- switch Sw is moved to a position to connect the upper terminal ofcoil 12ste ground through condenser 11 and a resistance R1.

In the embodiment of the invention disclosed tubes IRF, 2RF, SRF and thedetector tube DET are screen grid tubes having indirectly heatedcathodes as shown conventionally in the drawing. Tube 1AF and tubes 2AFand 2AF' are three electrode tubes, the cathodes of the latter beingdirectly heated by current passing therethrough. The plate or anode ofeach of the radio frequency tubes and the detector tube is connected tothe supply conductors 18 and 21 through the primary of the couplingtransformer 19, 24 and 25 respectively for the radio frequency tubes anda resistance R11 for the detector tube.

The heater for the cathodes oi.' the radio frequency, detector and firstaudio frequency tubes are connected to the secondary S of thetransformer T through a supply circuit 2D. A potentiometer P isconnected across the supply circuit and an adjustable contact or slider22 connects an intermediate point with the ground or negative side ofthe fllter.

The screen grids of tubes IRF, ZRF, and 3RF are connected to a Acommonconductor 28 and the screen grid of tube DET is connected to thisconductor through a high resistance R10 shunted by acondenser C10.Conductor 28 is connected to ground through a condenser` C4 and isconnected to a low voltage tap t of the filter F. Conductor 28 is alsoconnected to ground through three resistances R5, R6 and R7 arranged inseries. Resistance R6 is provided with a slider 30 which is connected tothe cathodes of'tubes lRF and 2RF and the cathodes of these tubes arealso connected to ground through a condenser C5.

Radio frequency transformer 24 has two secondaries 30' and 31ipspectively. Secondary 30 is grounded at one end through an adjustablecondenser 33 shunted by a trimming condenser 34 and at the other endgrounded through a xed condenser C6- shunted by a resistance R2, thisresistance and condenser also serving as aconnection to ground for oneend of `coil 31. The other end of coil 31 is connected to the grid oftube 3RF and also connected to ground through a tuning condenser 35shunted by a trimming condenser 36.

Cathode of tube 3R11' is' connected to ground denser C7.

6' through resistance R2 shunted by a .xed condenser C8 and the otherterminal is `connected to the grid of the detector tube and alsogtoground through a tuning condenser 37 shunted byfa trimming condenser 38.

The cathode of the detector tube is 'connected to ground throughresistance R9 shunted by a iixed condenser C9. J

The detector tube is coupled to the rst audio frequency amplifying tubeby a resistance coupling, comprising a resistance R11-in the platecircuit of the detector tube, a resistance R12 between the grid of thetube IAF and the ground, a coupling condenser C11 connected to this gridand to the plate of the detector tube through an i inductbnce I andcondensers C12 and C13 connectedrespectively between opposite ends ofthe inductance and ground.

The second audio frequency stage which in the present form of myinvention is the last stage, is al pushpull stage, comprising tubesv2AFand 2AF' connected to the preceding stage by a resistance coupling ofspecial construction. While my improved coupling may be used inconnection with systems other than the one comprising a radio frequencyand detector stage -above described, the entire system disclosed.represents one complete and operative embodiment of my invention. l

The cathode of tube IAF is connected to ground through a resistance R20.The plate of tube x1AF is connected to conductor18 through a couplingresistance R13, the conductor 18 being^connected through conductor 21`to an intermediate voltage tap t of the lter F. Plate of tube 1AF isconnected to the grid of tube 2AF by a coupling condenser C16. and thecathode of tube IAF is con' nected to the grid of tube 2AF' by acoupling condenser `C1'7. The grids of tube 2AF and 2AF are' connectedto ground respectively through resistance R14 and R15 which in thepresent embodiment of my invention are of equal values.

The filaments of tubes 2AF and 2AF.' are supplied with heating currentfrom the secondary S'f and across the supply circuit is connected apotentiometer P having a slider '39 which is,

connected to ground through a resistance' R18. The plates of tubes `2AFand 2AF are cori--v nected through an inductance I' an intermediate'point of which is tapped and connected to the.

high voltage 'tap t" pf the filter. The output circuit to the coil 33 ofthe loud speaker includes a condenser C19 and this circuit is connectedacross the inductance I.

The filter comprises inductances I3 and I4 inl between a point condenserC24 and the resistance R20 and -the intermediate tap for the platecircuit of the radio frequency tubes, the detector tube andthe rst audiofrequency tube is linwted through a resistance R8 shunted by a xed contoa point t between C23 and resistance R19, while the high voltage tap t"for the plates of the tubes 2AF and 2AF' is connected to a point betweeninductances I3 and I4.

In the operation of the resistance coupled push pull stage it will benoted that changes ofpotential of the grid of tube lAF produce oppositechanges of potential of the plate and of the cathode of this tube. Thusan increase in potential of the grid lowers the internal impedance ofthe tube, lowers the potential of the plate of the tube with respect toground at the same time, however, raising the potential of the cathodeof tube lAF. Thev changes in potential of the plate and cathode aretransmitted respectively to grids of tubes 2AF and 2AF through therespective condenser C16 and C17. y

'Ihe resistance ,R13 in the plate circuit of the tube 1AF is of the samevalue as the resistance R20 inthe cathode return circuit. Changes ofimpedance in the tube IAF due to changes of potential ci the grid ofthis tube will therefore effect equal and opposite changes of potentialatl the points X and X', that is, the plate and cathode respectively ofthe tube 1AF. The changes in potential of the grids of the push pulltubes 2AF and 2AF' will therefore be equal and opposite and the tubes2AF and 2AF' fwill each bear one half of the signal load.

One important feature of my invention is the construction of a push pullamplier of this character wherein variations of potential of thecurrents supplied to the tubes will not produce disturbing hum in theoutput circuit. Itawill, of course, be understood that the connectionsbetween tubes 2AF and 2AF' are such vthat disturb- 'ing variations due,'for example, to variations of the potential of the source supplied tothese particular tubes tends inherently to be eliminated. However, theportion of the system preceding this-stage may be affected by uctuationsfrom the source of supply so as to feed into the push pull stages humcurrents which would then be passed on to the loud speaker. It is onepurpose of my invention to so construct the system. disclosed, thatsubstantially no hum, arising in the stages preceding the push pullstage, is carried forward to the loud speaker.

Considering for themoment, the effect of variations of the potential ofthe output of the filter F on the plate circuit of tube 1AF, theseeffects comprise the direct effect caused by the supply of varyingcurrent from the tap t through resistance R13 to the plate of the tube1AF and the indirect eil'ect caused by the variations supplied to theplate circuit of the preceding tube o r tubes. Considering first thedirect effect; a momentary rise in potential ofthe source has the directeffect of raising the potential at the point X with respect to groundand thisl same rise has theeffect of raising the potential at point X'with respect to ground, but the magnitude ofthe rise of potential atthepoint X is much less than -the magnitude of rise at the point X.Considering the indirect eiects, a momentary rise of potential of thesource causes a rise in potential of the plate ofthe detector tube,which rise, transmitted through the condenser C11, raises the potentialof the grid o f tube IAF and this results in a lowering of the internalimpedance of the tube. This tends to decrease the potential at the pointX with'respect vto ground and to increase the potential at the effectsat the point X are opposed to one another; whereas the direct andindirect effects at the point X assist one another. In view, however, ofthe fact that the direct effect at the point X is much greater than thedirect effect at the point X', it is possible by taking away from thedirect effect at the point x and adding 1:6 theo direct effect at thepoint X' to make the combined directl and indirecteffects at the point Xequal to the combined direct and indirect effect at the point X. Withthis condition obtaining, the variations of potential of the grids oftube 2AF and 2AF' caused by these disturbing voltage variations will beequal and in phase with one another with the result that they willcancel one another in the push pull output circuit and no variationsfrom this source will appear in'the loud speaker circuit. If desired,the system ymay be so constructed as to feed variations of the desiredmagnitude and phase to the coil 3 3 of the loud speaker so as to buckout disturbing variations in the -loud speaker field coil F. The directand indirect effect at points X and X' may be` The indirect effect atthe point X is:

stantially the same frequency and phase; a momentary lessening of theimpedance of the tube IAF will have th effect of lowering the potentialat the point X and raising the potential at the point X'. However, thesimultaneous decrease in the impedance of the detector tube lowers thepotential of the detector tubefplate and consequently lowers thepotential of the grid of the tube IAF, thus tending to increase thinternal impedance of the tube lAF which results in a tendency to raisethel potential at the point X` and lower the potential at the point Xwith respect to ground. It will thus be seen that the directandfindirect effects of the variations in the tube impedance due tovariations in the cathode heating current are opposed .to one another atthe-point X and also at the point X'. It is thus possible substantiallyto eliminate hum variations at both of these points with the result thatno hum variations a-re transmitted to the grids of the push pull or totransmit to the grids of the -push pull variations of either one` of twooppo- 'site phases and to any desired magnitude.

If DV: represents the change in potential at the left hand side ofcondenser C11 the change in voltage at the point X due to DV: will bewhere a is the amplifying factor of the tube lAF,

and -DVzp respectively at the points X and X', of the alternatingcurrent for heating the cathode pFDVf R of the tube lAF.

R DV DV 3 l la Il' u I?x7 2 R where DV.; are variations of potential ofthe grid of tube lAF. The indirect effectsat the point X' are thenegative of expression 3 or passed onto the grid of tube IAE should'notvary greatly from It can readily be seen that by varying the terms ofthe Equations 1 to 5 this equality may be obtained in a varietyof ways.

The term DV; is dependent upon the magnitude of thel variationssupplied'by thev lter to the detector tube plate circuit and to someextent upon the character of and the current supplied to that I"part ofthe system preceding the detector stage.

In practice, I find when using a 327 tube as the tube -lAF thatresistances R12 and R13 may advantageously be made each of 10,000 ohms;where tube 2AF and 2AF' are each 345, I preferably make the resistanceseach 250,000 ohms with a tube 324 as the detector tube, R2 may be 1,000ohms, R9 20,000 ohms, C9 l mfd., R10 100,000 ohms, C10 .5 mfd., and R11250,000 ohms.

Having now described my invention what I desire to secure by LettersPatent is:

l. In a signal repeatingsystem, a .push pull stage comprising two vacuumtubes, a stage preceding said push pull stage comprising a vacuum tubehaving impedances in its plate supply and plate return circuits, ayconnection between a point of relatively negative potential of theformer of said impedances and the grid of one of said push pull tubes,^aconnection between a point of relatively positive potential of the laterof said Aimpezlancesand the grid of the other of said push pull tubes,means for supplying a plate circuit electrode of said preceding tubewith current sub-` ject to variations, and means for supplying the gridof said preceding. tube with variations of substantially the samefrequency and bearing a predetermined relation in phase and magnitude tosaid first named variations so as substantially to reduce disturbingvariations in the output of the system.-

2'.'In a signal repeating system, a push pull stagejcomprising a vacuumtubehaving equal resistances respectivelydn its plate supply and platereturn circuits,'a connection between the nega-tive side off the formerof said resistances andthe grid of onev o`f said push pull tubes and aconnection between the positive side of the latterof `said impedancesandthe grid of the other of said push pull tubes, means for supplying thetube. circuits with current subject to variations which tends to producedisturbing variations in the output circuit, and means for proportioningthe variations supplied to dierent tube circuits so that variationscarried forward t'o the grids of the push pull tubes are substantiallynulliedin the output of the system.

3. In a signal repeating system a push pull stage comprising two vacuumtubes, a stage preceding said push pull stage comprising a vacuum tubehaving impedances in its plate supply and plate return circuits, aconnection between a point of relatively negative potential of theformer of said impedances and the grid of one of said push pull tubesand a connection between a point of relatively positive potential of thelatter of said impedances and the grid of the other of said push pulltubes, means for supplying the plate circuit of said preceding tubewithcurrent subject to variations, and means for supplying the grid of saidpreceding tube with variations of substantially the same frequency andbearing a predetermined relation in phase and magnitude to said rstnamed variations so as to cause variations of substantially the samefrequency, phase and magnitude to be supplied to each of the grids ofthe push pull tubes.

4. In a signal repeating system, a push pull stage comprising two vacuumtubes, a stage preceding said push pull stage comprising a vacuum tubehaving impedances in its plate supply and plate return circuits, aconnection between a point of relatively negative potential of theformer of said impedances and the grid of one of said push pull tubes, aconnection between a point of relatively positive potential of thelatter of said impedances and the grid of the other of said push pulltubes, means for heating the cathode of said preceding tube with currentsubject to variations which tends to produce disturbing variations inthe plate circuit, and means for supplying the grid of said precedingtube with variations of substantially the same frequency and bearingsuch a relation in phase and magnitude to said rst named variations asto cause substantially no variations to be transmitted to the grids ofthe push pull tubes.

5. In a signalrepeating system, a push pull stage comprising two vacuumtubes, a stage preceding said push pull stage comprising a vacuum tubehaving impedances in its plate supply and plate return circuits, aconnection between a point of relatively negative potential of theformer of said impedances ,and the grid of one of said push pull tubes,a connection between a point of relatively positive potential of thelatter of said impedances and the grid of the other of said push pulltubes, means for heating the cathode of said preceding tube with currentsubject to variations which tends to produce disturbing variations inthe plate circuit, and means for supplying the grid of said precedingtube with variations of substantially the same frequency and bearingsuch a relation in phase and magnitude to said rst named variations asto cause variation of any desired magnitude and either of two oppositephases to be transmitted to the grids of said push pull tubes.

6.l In a signal repeating system, a push pull stage comprising twovacuum tubes, two stages in tandem preceding said push pull stages andeach comprising a vacuum tube, the later of said last named tubes havingequal impedances respectively inits plate supply and plate returncircuits, a connection between the negative side of said formerimpedance and the grid ofvone of said push pull tubes, a connectionbetween the positive side of the latter impedance and the grid of theother of said push pull tubes, and means for supplying the platecircuits of said preceding tubes with current subject to fluctuationswhich tend to cause disturbing variations in the plate circuits, theparts being so proportioned and arranged that the combined effect ofcurrent supplied to the earlier of said tandem tubes and that supplieddirectly to the plate circuit ofthe later of said tandem tubes is tocause variations of the same frequency, phase and magnitude to beimpressed on the grids of the push pull tubes.

7. In a signalvrepeating system, a push pull stage comprising two vacuumtubes, a stage preceding said push pull stage comprising a vacuum tubehaving equal impedances respectively in its plate supply and platereturn circuits, a connection between the negative side of the former ofsaid impedances and the grid of one of said push pull tubes and aconnection between the positive side of the latter of said impedancesand the grid of the other and said push pull tubes, means for supplyingthe plate circuit electrodes of said preceding tube with current subjectto variations, and means for supplying the grid of said preceding tubewith variations of substantially the same frequency and bearing apredetermined relation in phase and magnitude to said rst named vari;ations so as 'substantially to reduce disturbing variations in theoutput of the system.

HAROLD R, HAYDEN.

lll@

